What parents should know about autism and vaccines

By Asuka Koda, CNN

(CNN) — Until last week, parents who looked at the US Centers for Disease Control and Prevention’s website on autism and vaccines would see a few key points: Studies have not found links between vaccines and autism, nor have links been identified between any vaccine ingredients and autism.

At the direction of US Health and Human Services Secretary Robert F. Kennedy Jr., a longtime anti-vaccine activist, the CDC page now has a different message: “Scientific studies have not ruled out the possibility that infant vaccines contribute to the development of autism.”

HHS said the change was made to “reflect gold standard, evidence-based science.” But it drew a swift and sharp rebuke from doctors, scientists and advocates for people with autism, who say the website now includes misinformation and outdated and disproven ideas.

“Medical researchers across the globe have spent more than 25 years thoroughly studying this claim. All have come to the same conclusion: Vaccines are not linked to autism,” according to a statement from more than 60 organizations, including the American Academy of Pediatrics, the American Medical Association and the Autism Science Foundation.

Here’s what to know about what’s changed and what hasn’t.

What does research into autism and vaccines show?

Independent researchers across seven countries have conducted more than 40 studies involving over 5.6 million people to conclude that there is no link between vaccines and autism, said Dr. Sean O’Leary, a professor of pediatrics and infectious diseases at the University of Colorado Denver Anschutz Medical Campus and Children’s Hospital Colorado.

Links between vaccines and autism have “been debunked many times,” O’Leary, who chairs the Committee on Infectious Diseases for the American Academy of Pediatrics, said at a news briefing last week. “It is considered settled science.”

Dr. Alycia Halladay, the chief science officer for the Autism Science Foundation, noted that experiments in countries including Denmark, Sweden, Finland, Israel and Japan collected data from large groups of people and tracked their vaccination patterns and whether they had an autism diagnosis.

“All of those studies have shown no link between vaccines and autism,” she said. “It remains the number one studied environmental factor in autism, and there is no link whatsoever.”

More research is needed on many of the other purported causes of autism, she said, “but vaccines have 1,000% been exonerated” as a factor.

On Monday, 30 autism and disability organizations said linking autism and vaccines confuses parents. They called on the CDC “to revert the website to its previous version, commit to vaccine education initiatives around the country that emphasize the high-quality, scientific evidence that vaccines do not cause autism, and invest in research projects and initiatives that are responsive to the needs of autistic people and their families.”

Where did claims about autism and vaccines start?

The pervasive myth linking vaccines and autism largely grew out of a 1998 study by a British gastroenterologist named Dr. Andrew Wakefield that tied the measles, mumps and rubella shot to autism.

But the paper had major flaws: It included only about a dozen children and no control group; financial conflicts of interest; and fabricated data. Wakefield has long pushed back on criticisms of the study, but the paper was retracted in 2010 and Wakefield’s medical license was revoked.

Many parents want to find an explanation for what was causing their children’s autism and to have “someone to blame,” Halladay said — and shots quickly became a scapegoat.

“The reality is that getting vaccinated isn’t exactly a fun procedure to begin with. You take your child to a pediatrician’s office, and they get a shot. They’re crying. It’s loud. It’s not a pleasant experience,” Halladay said.

If parents can believe that there is “something that they might be able to do to stop [their child’s autism], and also get to avoid those visits, they’ll do it. It’s really preying on the fears of parents and the idea that parents can do something to prevent their child’s autism. It’s taking advantage of parents who are vulnerable in that way.”

After Wakefield’s paper was published, a flurry of research was conducted around the world to try to replicate the results, but the research came to much different conclusions than Wakefield’s paper.

“It was retracted, but at the same time … the bell had been rung,” Halladay said: The claims of a link between autism and vaccines had taken hold.

What causes autism?

The autism diagnosis rate has increased among US children, continuing a long-term trend that experts have largely attributed to better understanding of and screening for the condition. About 1 in every 31 children was diagnosed with autism by age 8 in 2022, up from 1 in 36 in 2020.

Autism is complex, encompassing a spectrum of people who “are able to communicate and also have cognitive abilities and live independently, all the way to those needing 24/7 care,” Halladay said. This diversity is reflected in how there “can’t possibly be one cause for autism.”

Autism is highly genetic, and more than 250 genes have been found to be associated with it. “In about 15% to 20% of cases, we can find a single gene that causes autism, and in other cases, there may be multiple genetic mutations interacting to cause autism,” O’Leary said. “Genes that are associated with autism are highly expressed during fetal brain development and pregnancy, and they converge on biological pathways that involve how nerve cells communicate with each other.”

Some environmental factors, including maternal illness during pregnancy, can also “increase the probability of an autism diagnosis,” Halladay said. This is one of the reasons it’s important for pregnant women to stay up to date on recommended vaccines.

“If you have measles, you have a full-body rash. You have a fever that runs for days and days. You feel sick from being exhausted to having a fuzzy head to having respiratory problems to nausea for days and days, not just a few hours,” Halladay said. “ So this is much more serious than any reaction that you might have to the vaccine, which isn’t universal. Some people may have a fever for a few hours, but it’s nothing like getting actually sick with these diseases.”

Other factors that have been associated with autism include premature birth, parents who are older at the time of conception, fever during pregnancy and metabolic disorders such as gestational diabetes.

Where can families get vaccine information?

The update to the CDC’s website was not science-based, Halladay said, and that can be confusing.

“We’ve been telling families for years to go to the CDC website, the CDC website has the information that you need, and now, all of a sudden, the information that was posted did not come from the CDC,” Halladay said.

“This current information was not vetted by any of the scientists from the Centers for Disease Control. It was shared by administrators at the Department of Health and Human Services, so it really isn’t scientific information.”

Professional medical organizations – including the Autism Science Foundation, the Autism Society of America, Autism Speaks, the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists – are other places to find accurate information on autism and vaccines.

Peer countries in Europe and the UK, Canada and Mexico all “have stood by the statement that vaccines do not cause autism,” Halladay said.

Halladay’s other advice to parents: “Trust your pediatrician. These are the people that know you. These are the people that see you in person and you know and can give you the best advice.”

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